Blower

ABSTRACT

A blower includes a fan that has blades and generates an air flow by rotating. Each of the blades has a front edge and a serration provided at least in a part of the front edge. The serration has tip portions and recessed portions arranged alternately with each other. Each of the blades has a negative pressure surface and one or more ribs protruding from the negative pressure surface. Each of the ribs extends from a corresponding one of the recessed portions, which is designated as a starting point, toward a rear edge of a corresponding one of the blades.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Application No. 2014-190016 filed on Sep. 18, 2014 and Japanese Patent Application No. 2015-083573 filed on Apr. 15, 2015, the disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a blower.

BACKGROUND ART

A conventional axial blower includes blades, and each of the blades has a front edge provided with a serration (see Patent Literatures 1, 2, for example). A rounding flow of air flowing from an oblique portion of the serration to a negative pressure surface of each of the blades is caused due to the serration when an air flow flows to the front edge of each of the blades. The rounding flow is a downward flow flowing downward toward the negative pressure surface. The downward flow presses a main flow, which flows on the negative pressure surface of each blade from a tip portion of the serration toward the rear edge of the blade, against the negative pressure surface of the blade, and thereby the main flow is prevented from separating from the negative pressure surface. As a result, turbulence of air flows adjacent to the blade surface of the blade is moderated, a pressure variation on the blade surface is suppressed, and thereby noise caused in an axial blower can be reduced.

PRIOR ART LITERATURES Patent Literature

-   Patent Literature 1: JP 2000-87898 A -   Patent Literature 2: JP 2014-88788 A

SUMMARY OF INVENTION

However, as a result of a test of the effects of the foregoing serration, which was actually conducted by the inventors of the present disclosure, it was found that expected effects could not be acquired fully for the reasons described below.

That is, the directions of air flows on a blade surface of each blade vary according to positions on the blade surface in a fan radial direction. Therefore, main flows, which respectively involve downward flows generated by the serration, collide with each other on the negative pressure surface, and thereby turbulence of air flows occurs. As a result, a suppressing effect that prevents the main flows from separating from the negative pressure surface is not fully exerted. Such a disadvantage occurs not only in an axial blower but also in other blowers in which the blades are serrated, such as a centrifugal fan and a cross-flow fan.

It is an objective of the present disclosure to provide a blower that can improve a serration effect.

A blower according to a first aspect of the present disclosure includes a fan that has blades and generates an air flow by rotating. Each of the blades has a front edge and a serration provided at least in a part of the front edge. The serration has tip portions and recessed portions arranged alternately with each other. Each of the blades has a negative pressure surface and one or more ribs protruding from the negative pressure surface. Each of the ribs extends from a corresponding one of the recessed portions, which is designated as a starting point, to a rear edge of corresponding one of the blades.

According to the above-described configuration, a main flow involving a downward flow is generated between adjacent two of the tip portions, and the main flow flows along the ribs that extend from the recessed portions toward the rear edges respectively, on a side adjacent to the negative pressure surface of the blades. As a result, directions of air flows flowing on the negative pressure surface can be adjusted to be parallel to each other. Thus, a collision between main flows, which respectively involve downward flows generated by the serration, is suppressed, and thereby a suppressing effect that prevents the main flows from separating from the negative pressure surface can be exerted.

Alternatively, a blower according to a second aspect of the present disclosure includes an axial fan that has blades arranged around a fan axis and rotates around the fan axis. Each of the blades has a negative pressure surface, a positive pressure surface, a front edge, and a rear edge. The negative pressure surface forms a blade surface on one side in a fan axial direction that is an upstream side in a flow direction of air. The positive pressure surface forms a blade surface on an opposite side of the negative pressure surface. The front edge is located on a front side in a rotating direction. The rear edge is located on a rear side in the rotating direction. The front edge of each of the blades is provided with a serration that has tip portions and recessed portions. The tip portions and the recessed portions are arranged alternately with each other along the front edge. The negative pressure surface of each of the blades is provided with one or more ribs protruding from the negative pressure surface. Each of the ribs extends from a corresponding one of the recessed portions, which is designated as a starting point, to the rear edge.

According to the above-described configuration, the directions of air flows flowing on the negative pressure surface can be adjusted to be parallel to each other by the ribs. Accordingly, a collision between main flows, which are generated by the serration and involve downward flows respectively, can be suppressed. Thus, a suppressing effect, which prevents the main flows from separating from the negative pressure surface due to the downward flows generated by the serration, can be exerted.

Alternatively, a blower according to a third aspect of the present disclosure includes an axial fan that has blades arranged around a fan axis and rotates around the fan axis. Each of the blades has a negative pressure surface, a positive pressure surface, a front edge, and a rear edge. The negative pressure surface forms a blade surface on one side in a fan axial direction that is an upstream side in a flow direction of air. The positive pressure surface forms a blade surface on an opposite side of the negative pressure surface. The front edge is located on a front side in a rotating direction. The rear edge is located on a rear side in the rotating direction. The front edge of each of the blades is provided with a serration that has tip portions and recessed portions arranged alternately with each other. The tip portions and the recessed portions are arranged alternately with each other along the front edge. The negative pressure surface of each of the blades is provided with first ribs protruding from the negative pressure surface. The positive pressure surface of each of the blades is provided with second ribs protruding from the positive pressure surface. Each of the first ribs and the second ribs extends in a circumferential direction of a circle centering on the fan axis, from a corresponding one of the recessed portions, which is designated as a starting point, to the rear edge, which is designated as an end point, In an area in which the serration is provided, a portion of the serration forming area located on an inner side of a center of the serration forming area in a radial direction of the axial fan is defined as an inner peripheral portion of the serration, and a portion of the serration forming area located on an outer side of the center of the serration forming area in the radial direction of the axial fan is defined as an outer peripheral portion of the serration. A total quantity of the first ribs and the second ribs provided in the outer peripheral portion of the serration is larger than a total quantity of the first ribs and the second ribs provided in the inner peripheral portion of the serration. A quantity of the second ribs is larger than a quantity of the first ribs.

According to the above-described configuration, the second ribs are provided in a part of the recessed portions provided with the serration, and a quantity of the second ribs is larger than a quantity of the first ribs. As a result, directions of the air flows flowing on the positive pressure surface can be adjusted to be parallel to each other. Therefore, directions of the air flows emitted from the rear edge can be the same on a side adjacent to the negative pressure surface and on a side adjacent to the positive pressure surface. Accordingly, air flows released from the rear edge can be stable.

Thus, according to the present disclosure, a serration effect can be improved as compared to a case having no rib.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view illustrating an axial blower according to a first embodiment.

FIG. 2 is a cross-sectional view taken along a line II-II shown in FIG. 1.

FIG. 3 is a top view illustrating a blade when viewed from an upstream side of an air flow in a fan axial direction.

FIG. 4 is a perspective view illustrating the blade in FIG. 3.

FIG. 5 is a cross-sectional view taken along a line V-V shown in FIG. 3.

FIG. 6 is a diagram illustrating air flows in a portion VI shown in FIG. 4.

FIG. 7 is a perspective view illustrating a blade of an axial blower according to a comparative example.

FIG. 8 is a diagram illustrating air flows in a portion VIII shown in FIG. 7.

FIG. 9 is a perspective view illustrating a blade according to a second embodiment.

FIG. 10 is a perspective view illustrating a blade according to a third embodiment.

FIG. 11 is a perspective view illustrating a blade according to a fourth embodiment.

FIG. 12 is a perspective view illustrating a blade according to a fifth embodiment.

FIG. 13 is a perspective view illustrating a blade according to a sixth embodiment.

FIG. 14 is a diagram showing measurement results of noise level in the axial blowers according to the first embodiment, sixth embodiment, and comparative example.

FIG. 15 is a perspective view illustrating a blade according to a seventh embodiment.

FIG. 16 is a cross-sectional view taken along a line XVI-XVI shown in FIG. 15.

FIG. 17 is a perspective view illustrating a blade according to another embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described hereafter referring to drawings. In the embodiments, a part that corresponds to or equivalents to a matter described in a preceding embodiment may be assigned with the same reference number. When only a part of a configuration is described in an embodiment, parts described in preceding embodiments may be applied to the other parts of the configuration.

First Embodiment

In the present embodiment, a description will be given using an example where a blower according to the present disclosure is applied to an axial blower 1 that blows air in an axial direction. First, referring to FIGS. 1, 2, the overall configuration of the axial blower 1 according to the present embodiment will be described. FIG. 1 is a front view of the axial blower 1 viewed from the upstream of air flow. In FIGS. 1, 2, a double-headed arrow D1 indicating an up-down direction, a double-headed arrow D2 indicating a left-right direction, and a double-headed arrow D3 indicating a front-rear direction are viewed when the axial blower 1 is mounted in a vehicle.

The axial blower 1 according to the present embodiment is a blower for a vehicle. Specifically, the axial blower 1 is mounted in a radiator 2 for a vehicle and supplies air to the radiator 2. The radiator 2 is a heat exchanger that cools coolant water through heat exchange between air and coolant water for an engine used for running vehicle.

As shown in FIG. 2, the axial blower 1 is disposed on the rear side of the vehicle further than the radiator 2 and downstream in the air flow passing through the radiator 2. The axial blower 1 draws air passed through the radiator 2 and blows the air out towards the rear of the vehicle.

The axial blower 1 includes an axial fan 10, a shroud 20, and a motor 30. The motor 30 is an electric motor that rotates and drives the axial fan 10. The motor 30 has a rotary shaft 31. The motor 30 is fixed to the shroud 20 by a stay 32. The stay 32 is a support member that supports the motor 30.

The axial fan 10 rotates around a fan axis CL1 of the axial fan 10 by means of the motor 30. The axial fan 10 rotates in a direction indicated by an arrow DR1 in FIG. 1. The axial fan 10 includes a motor mounting part 11, blades 12, and a ring part 13.

The motor mounting part 11 is a cylindrical member mounted on the rotary shaft 31 of the motor 30. The motor mounting part 11 supports the blades 12 on the outside of the sidewall of the motor mounting part 11. The motor mounting part 11 is also referred to as a boss part.

The blades 12 radially extend from the motor mounting part 11. The blades 12 are mainly arranged at equal intervals around the motor mounting part 11.

The ring part 13 is an annular member provided on the outer peripheral part of the axial fan 10. More specifically, the ring part 13 is a member having an annular shape about the fan axis CL1 as shown in FIG. 1 and a cylindrical shape extending by a specified length in a fan axial direction as shown in FIG. 2.

The ring part 13 has a sidewall 131 having a cylindrical shape. The ring part 13 is connected to the respective outer peripheral ends of the blades 12. In other words, the sidewall 131 of the ring part 13 has connection parts 132 that are respectively connected to the blades 12. Here, “connection” means, not only a state in which the separately formed blades 12 and the ring part 13 are connected, but also a state in which the integrally formed blades 12 and the ring part 13 are continuous. In the present embodiment, the motor mounting part 11, the blades 12, and the ring part 13 are integrally molded with a resin such as polypropylene.

The ring part 13 has a bell-mouth 133 that is provided in an end portion of the sidewall 131 on an upstream side in a flow direction of air and that has an arc shape in cross section.

The shroud 20 forms an air passage 20 c through which air that has passed through the radiator 2 flows toward the axial fan 10. The shroud 20 is molded with a resin such as polypropylene. In the shroud 20, an air inlet 20 a through which air flows is formed on the radiator 2 side and, on the opposite side, an air outlet 20 b through which air flows out is formed. The axial fan 10 is disposed in the shroud 20 on a side adjacent to the air outlet 20 b.

More specifically, the shroud 20 includes an air inflow part 21, air outflow part 22, and intermediate part 23.

The air inflow part 21 is the portion in which the air inlet 20 a is formed. The air inflow side of the air inflow part 21 is connected to the radiator 2. The air inlet 20 a is open in the fan axial direction and opposite the radiator 2. A center of the air inlet 20 a coincides with the fan axis CL1.

The shape of the air inlet 20 a corresponds to the shape of the radiator 2. That is, the air inlet 20 a has a horizontally-long rectangular shape, in which an edge extending in a vehicle width direction (i.e., the left-right direction) D2 is longer than an edge extending in the up-down direction D1 of the vehicle, when viewed in the fan axial direction, as shown in FIG. 1. Accordingly, a distance L2 between an inner wall of the air inflow part 21 and the axial fan 10 in the left-right direction D2 of the vehicle is greater than a distance L1 between the inner wall of the air inflow part 21 and the axial fan 10 in the up-down direction D1.

The air outflow part 22 is a portion in which the air outlet 20 b is formed, in which the axial fan 10 is disposed. The axial fan 10 rotates and, therefore, in the air outflow part 22, the ring part 13 and shroud 20 are separated from the axial fan 10 such that a clearance part 24 is formed. That is, the air outflow part 22 in the present embodiment configures a cylindrical portion facing the ring part 13 on a radial outer side of the ring part 13.

The air outlet 20 b is open in the fan axial direction. The shape of the air outlet 20 b corresponds to the shape of the axial fan 10. That is, the air outlet 20 b has a circular shape when viewed in the fan axial direction. A center of the air outlet 20 b coincides with the fan axis CL1.

In the present embodiment, a most downstream portion 221 of the air outflow part 22 in the air flow protrudes further inwards than a portion 222 that faces the ring part 13, such that the radius of the air outlet 20 b is equal to the inside diameter of the downstream end of the ring part 13. An air inlet 25, through which air flows into the clearance part 24, is formed between the most downstream portion 221 furthest downstream of the air outflow part 22 and the ring part 13.

The intermediate part 23 forms an air passage that guides air from the air inflow part 21 to the air outflow part 22. In the intermediate part 23, the distance L2 between the inner wall of the air inflow part 21 and the axial fan 10 in the left-right direction D2 gradually decreases toward the air outflow part 22 from the air inflow part 21. Therefore, a passage cross-sectional area (i.e., opening area) of the intermediate part 23 gradually decreases toward the air outflow part 22 from the air inflow part 21.

A passage cross-sectional area of the air passage 20 c provided in the shroud 20 decreases from the air inflow part 21 toward the air outflow part 22 since the intermediate part 23 is interposed between the air inflow part 21 and the air outflow part 22.

In the axial blower 1 of such a configuration, when the axial fan 10 is rotated by rotation of the rotary shaft 31 of the motor 30, air that has passed through the radiator 2 is drawn into the axial fan 10 and blown out parallel to the fan axis CL1 from the axial fan 10, as indicated by an arrow F1 in FIG. 2.

At this time, air in the air passage 20 c is sent to the air outlet 20 b by rotation of the axial fan 10. Therefore, a pressure at a position A1 in the shroud 20 on the side adjacent to the air outlet 20 b is higher than a pressure at a position A2 on the air suction side of the axial fan 10. Accordingly, as indicated by an arrow F2 shown in FIG. 2, a part of air from the axial fan 10 passes through the clearance part 24 from the air inlet 25, and flows back into the suction side of the axial fan 10. The back flow shown by the arrow F2 is reduced according to the present embodiment as compared to a case having no ring part 13, since the ring part 13 is provided in the outer periphery of the axial fan 10. In addition, the bell-mouth 133 is provided in the end portion of the ring part 13. Therefore, turbulence on the air inflow side of the axial fan 10 into which the back flow shown by the arrow F2 joins is reduced as compared to a case having no bell-mouth 133.

Main characteristics of the axial blower 1 according to the present embodiment will be hereafter described referring to FIGS. 3, 4, 5.

As shown in FIG. 5, each of the blades 12 has blade surfaces, one of which is a negative pressure surface 121 disposed upstream in the air flow in the fan axial direction, and the other of which is a positive pressure surface 122 disposed on an opposite side the negative pressure surface 121. In other words, each of the blades 12 has a negative pressure surface 121 forming a blade surface on one side in the fan axial direction that is an upstream side in the flow direction of air, and a positive pressure surface 122 forming a blade surface on the other side in the fan axial direction that is the opposite side of the negative pressure surface 121. Each of the blades 12 has a front edge 123 located on a front side in a rotating direction DR1, and a rear edge 124 located on a rear side in the rotating direction DR1. Each of the blades 12 has a specified attack angle α and a specified blade chord length L12.

As shown in FIGS. 3, 4, each of the blades 12 has a front edge 123, and the front edge 123 has a serration 40. The serration 40 has tip portions 41 and recessed portions 42. The tip portions 41 and the recessed portions 42 are arranged alternately with each other along the front edge 123. In addition, the negative pressure surface 121 of each blade 12 has ribs 51 protruding from the negative pressure surface 121.

The serration 40 is configured by protruding portions that have a triangular shape and are arranged adjacent to each other. Each protruding portion has the tip portion 41 that includes a tip of the protruding portion. The recessed portion 42 is defined as a hollow provided between adjacent two of the protruding portions.

Each rib 51 extends toward the rear edge 124 from its respective recessed portion 42, as a starting point 51 a, of the front edge 123. In other words, each rib 51 extends toward the rear edge 124 from the position corresponding to the recessed portion 42 of the front edge 123, as the starting point 51 a. Specifically, the position corresponding to the recessed portion 42 of the front edge 123 is the starting point 51 a, and the position on the rear edge 124 is an end point 51 b. For example, each rib 51 continuously extends from the starting point 51 a to the end point 51 b. In other words, each rib 51 is disposed all the way from the recessed portion 42 of the front edge 123 to the rear edge 124. The ribs 51 extend parallel to one another.

More specifically, the starting point 51 a of each rib 51 is located in a deepest portion of the recessed portion 42. The end point 51 b is the point that is located on the rear edge 124 corresponding to the starting point 51 a in a circumferential direction of a circle centering on the fan axis CL1. That is, the ribs 51 extend parallel to each other in the circumferential direction of the circle centering on the fan axis CL1 of the axial fan 10. In other words, a center axis of each of the ribs 51 centers on the fan axis CL1 of the axial fan 10 and extends to trace an arc passing the starting point to which a corresponding one of the ribs 51 is connected.

In the present embodiment, the ribs 51 are provided in all the recessed portions 42. Therefore, the quantity of recessed portions 42 in the serration 40 and a quantity of the ribs 51 are equal to each other.

In addition, the height h1 of each rib 51 is set higher than the boundary layer of air flow, which is formed on the blade surface. In addition, in terms of relative velocity (with respect to each blade 12) of air flow around the blade 12, an inner peripheral side of the blade 12 is lower than an outer peripheral side. A main flow F4, which flows on the negative pressure surface 121 while involving a downward flow F5 as described after, thereby becomes harder to be separated from the negative pressure surface 121 as approaching the inner end of the blade 12. As a result, an effect due to the ribs 51 described later can be obtained even in a case where a height h1 of the ribs 51 on the inner peripheral side of the blade 12 is lower than a height h1 of the ribs 51 on the outer peripheral side of the blade 12.

According to the present embodiment, the heights h1 of the ribs 51 are set to decrease from the outer peripheral side toward the inner peripheral side of the axial fan 10. In other words, the heights h1 of the ribs 51 are set to increase from a radial inner side (i.e., the inner peripheral side) of the axial fan 10 toward a radial outer side (i.e., the outer peripheral side) of the axial fan 10.

Here, a comparison is made between the axial blower 1 according to the present embodiment and an axial blower J1 in a comparative example shown in FIG. 7. The axial blower J1 in the comparative example differs from the axial blower 1 in the present embodiment only in that the axial blower J1 has no rib 51 in the negative pressure surface 121 of each blade 12.

In the axial blower 1 according to the present embodiment shown in FIGS. 1, 2 and the axial blower J1 in the comparative example, the air flow entering the axial fan 10 has a velocity component in a direction perpendicular to the fan axis CL1 of the axial fan 10, that is, in the direction of the fan axis CL1. In terms of relative velocity of air flow, which passes through the axial fan 10, with respect to each blade, the inner peripheral side of the axial fan 10 is higher than the outer peripheral side of the axial fan 10. As a result, an air flow in the outer peripheral portion of the axial fan 10 becomes contracted flow. One of the factors causing contracted flow is that a passage cross-sectional area of the air passage in the shroud 20 decreases from the air inflow part 21 toward the air outflow part 22.

Furthermore, in the axial blower 1 according to the present embodiment and the axial blower J1 in the comparative example, the distance L2 between the axial fan 10 and the inner wall of the air inflow part 21 in the left-right direction D2 is greater than the distance L1 between the axial fan 10 and the inner wall of the air inflow part 21 in the up-down direction D1. Therefore, air flow passing through the axial fan 10 is more likely to become contracted flow in the left-right direction. That is, in the configuration of the present embodiment, the degree of reduction in the passage cross-sectional area of the air passage in the shroud 20 in the left-right direction is greater than that in the up-down direction. Therefore, contracted flow is more likely to occur in the left-right direction.

In addition, in the axial blower 1 according to the present embodiment and the axial blower J1 in the comparative example, stagnation of air flow occurs in an area A3 (see FIG. 2) on the air-flow downstream side of the connection part 132 near the inner periphery of the ring part 13. An occurrence of the contracted flow on the outer peripheral side of the axial fan 10 is promoted since the above-described velocity difference between the outer peripheral side and the inner peripheral side of the axial fan 10 increases due to an occurrence of stagnation. As a result, directions of air flows on the blade surface of each blade 12 varies depending on positions of the blade surface in a radial direction of the fan, according to the axial blower 1 of the present embodiment and the axial blower J1 of the comparative example. Specifically, as shown in FIGS. 6, 8, the direction of an air flow F3 flowing on each blade 12 differs between the inner peripheral side and the outer peripheral side of the blade 12. An air flow F3 a flowing on the inner peripheral side of the blade 12 is directed in a circumferential direction around the fan axis CL1. An air flow F3 b flowing on the outer peripheral side of the blade 12 is directed further toward the fan axis CL1 than the air flow F3 a flowing on the inner peripheral side of the blade 12.

Therefore, as shown in FIG. 8, in the comparative example, the main flows F4 involving the downward flows F5 generated by the serration 40 collide with each other on the negative pressure surface 121, resulting in an air flow turbulence F6. Consequently, the effect of the serration 40, that is, the effect of restricting separation of each main flow F4 on the negative pressure surface 121 is not fully exhibited. Each of the downward flows F5 in FIG. 8 is an air flow declining toward the negative pressure surface 121 after encountering the side adjacent to the negative pressure surface 121 of each blade 12 from an inclining portion of the tip portion 41 when the air flow F3 flows onto the front edge 123 of each blade 12. In addition, each of the main flows F4 in FIG. 8 is an air flow flowing on the negative pressure surface 121 of the blade 12 from the apex of the tip portion 41 toward the rear edge 124 of the blade 12. In addition, dashed lines in FIG. 8 indicate a projection line of the respective flowing directions of the main flows F4 on the negative pressure surface 121. The dashed lines in FIG. 6 are similar to those in FIG. 8.

In contrast, as shown in FIG. 6, the directions of air flows flowing on the negative pressure surface 121 can be adjusted to be parallel to each other by the ribs 51 according to the present embodiment. As a result, a collision between the main flows F4 that respectively involve the downward flows F5 generated by the serration 40 can be suppressed. Therefore, the suppressing effect, which prevents the main flows F4 from separating from the negative pressure surface 121 due to the downward flows F5 generated by the serration 40, can be exerted. Thus, noise can be reduced, since turbulence of air flows adjacent to the blade surface can be reduced and thereby a pressure variation on the blade surface causing the noise can be suppressed.

Here, each of the tip portions 41 of the serration 40 is a part that, when air flow flowing onto the front edge 123 of each blade 12 encounters the side adjacent to the negative pressure surface 121 of the blade 12, generates a downward flow (a vertical vortex) declining toward the side adjacent to the negative pressure surface 121 of the blade 12.

In contrast, each of the recessed portions 42 of the serration 40 is a part that does not contribute to generation of downward flow on the side adjacent to the negative pressure surface 121 of each blade 12 in the serration 40, but agitates downward flow on the negative pressures surface 121 side of the blade 12.

Then, the present embodiment sets the starting point 51 a for each rib 51 at the recessed portion 42 of the serration 40, which recessed portion 42 does not contribute to generation of downward flow. As a result, the ribs 51 themselves do not block generation of downward flow in the serration 40, and therefore the suppressing effect that prevents the main flows from separating from the serration 40 can be exerted certainly.

In addition, in the present embodiment, the ribs 51 are provided on the side adjacent to the negative pressure surface 121 of each blade 12, thereby restricting interference between air flow along the surface of the blade 12 and air flow on the outside of the blade 12 (e.g., an air flow flowing in the clearance part 24). Accordingly, generation of turbulence noise (i.e., noise in a wide band), resulting from air flow turbulence on the surface of each blade 12 can be reduced. Furthermore, generation of rotation noise, resulting from interference between air flow along each blade surface and air flow on the outside of the blade 12 can be reduced.

In particular, in the present embodiment, the height of each rib 51 in the protruding direction increases as the rib extends from the radial inside to the radial outside of the axial fan 10. Therefore, rotation noise resulting from interference between air flow along each blade surface and air flow on the outside of the blade 12 can be reduced more effectively.

Second Embodiment

The quantity of the ribs 51 in the present embodiment is smaller than in the first embodiment, but the other configurations in the present embodiment are identical to those in the first embodiment.

As shown in FIG. 9, in the present embodiment, ribs 51 are provided only for every other recessed portion 42 of recessed portions 42 of the serration 40. As just described, according to the present embodiment, a quantity of the recessed portions 42 and a quantity of the ribs 51 are not equal to each other such that the quantity of the ribs 51 is smaller than the quantity of recessed portions 42.

Even if the quantity of the ribs 51 is smaller than the quantity of recessed portions 42 as in the present embodiment, the effect of restricting separation of main flows F4 on the negative pressure surfaces 121, which is caused by downward flows F5 created by the serration 40, can be exhibited fully, compared to a case where ribs 51 are not provided on the negative pressure surfaces 121.

In addition, an additional fixed wall surface is generated in air flows flowing on the negative pressure surface 121 when providing the ribs 51 in the negative pressure surface 121, and thereby an additional vortex may be occurred by the ribs 51. Therefore, it is not preferable to provide the ribs 51 unnecessarily, and a quantity of the ribs 51 is preferably set as small as possible as in the present embodiment. Therefore, according to the present embodiment, generation of additional vortexes from the ribs 51 can be reduced, in comparison with a case where ribs 51 are provided in all the recessed portions 42.

The present embodiment is effective in a case that a difference in direction of air flow on the outer peripheral side and the inner peripheral side of each blade 12 is small, and that the effect of restricting separation of each main flow F4 on negative pressure surfaces 121 is fully exhibited not by providing the ribs 51 for all the recessed portions 42, but by providing the ribs 51 for only some of the recessed portions 42.

Third Embodiment

As with the second embodiment, the quantity of the ribs 51 in the present embodiment is smaller than that in the first embodiment. In addition, the quantity of the ribs 51 on the outer peripheral portion of the serration 40 is larger than the quantity of the ribs 51 on the outer peripheral portion of the serration 40. Other configurations in the present embodiment are identical to those in the first embodiment.

As shown in FIG. 10, in the present embodiment, ribs 51 are provided in recessed portions 42 located in the first to fifth positions from the outer peripheral side, other than recessed portions 42 located in the first and second positions from the inner peripheral side.

Here, the inner-peripheral-side portion of an axial fan 10 from the position of the radial center of the axial fan 10 in the area in which the serration 40 is formed is referred to as an inner peripheral portion of the serration 40. The outer-peripheral-side portion of the axial fan 10 from the position of the radial center of the axial fan 10 in the area in which the serration 40 is provided is referred to as the outer peripheral portion of the serration 40. In this case, in the present embodiment, the recessed portions 42 in the first, second, and third positions from the outer peripheral side are located in the outer peripheral portion of the serration 40, whereas the recessed portions 42 in the first, second, and third positions from the inner peripheral side are located in the inner peripheral portion of the serration 40. In the present embodiment, three ribs 51 are provided on the outer peripheral portion of the serration 40 and one rib 51 is provided on the inner peripheral portion of the serration 40. Therefore, in the present embodiment, the quantity of the ribs 51 on the outer peripheral portion of the serration 40 is larger than the quantity of the ribs 51 on the inner peripheral portion of the serration 40.

As described above, in the present embodiment, the ribs 51 are provided in only some recessed portions 42 of the serration 40. Therefore, the present embodiment yields the same effects as those in the second embodiment.

Furthermore, in the present embodiment, the outer peripheral portion of the serration 40 has more ribs 51 than the inner peripheral portion of the serration 40. A suppressing effect that prevents the main flows F4 from separating from the negative pressure surface 121 can be exerted sufficiently on a condition that the ribs 51 are provided in only some of the recessed portions 42, for the reason explained below.

A contracted flow is less likely to be caused on the inner peripheral side of the axial fan 10 since the inner peripheral side is hardly affected by stagnation that may occur near a ring portion 13. A contracted flow is likely to be caused on the outer peripheral side of the axial fan 10 since the outer peripheral side is easily affected by stagnation that may occur near the ring portion 13. Then, a quantity of the ribs 51 provided in the inner peripheral portion of the serration 40 is decreased, and a quantity of the ribs 51 provided in the outer peripheral portion of the serration 40 is increased. As a result, directions of air flows flowing on the negative pressure surface 121 can be adjusted to be parallel to each other, and thereby a collision between the main flows, which involve the downward flows caused by the serration 40, can be suppressed.

In the present embodiment, three of the ribs 51 are provided in the outer peripheral portion of each serration 40, and a single one of the ribs 51 is provided in the inner peripheral portion of the serration 40. However, quantities of the ribs 51 respectively provided in the outer peripheral portion and the inner peripheral portion of the serration 40 may be changed as long as a quantity of the ribs 51 provided on the outer peripheral portion is larger than a quantity of the ribs 51 provided on the inner peripheral portion. For example, ribs 51 may be provided in only recessed portions 42 located in the first, second, and third positions from the outer peripheral side, such that the outer peripheral portion of the serration 40 has three ribs 51 and the inner peripheral portion of the serration 40 has no ribs.

Fourth Embodiment

In the present embodiment, ribs 52 are added on the positive pressure surface 122 of each blade 12. The other configurations in the present embodiment are identical to those in the first embodiment.

As shown in FIG. 11, in the present embodiment, as with the first embodiment, on the negative pressure surface 121 of each blade 12, ribs 51 are provided in all recessed portions 42 of the serration 40. In addition, on the positive pressure surface 122 of the blade 12, ribs 52 are provided in all recessed portions 42 of the serration 40. Hereinafter, a rib 51 provided in the negative pressure surface 121 is referred to as a first rib 51, and a rib 52 provided in the positive pressure surface 122 is referred to as a second rib 52.

As with the first embodiment, each of the first ribs 51 extends continuously from a corresponding one of the recessed portions 42 of a front edge 123, which is designated as a starting point 52 a, to the rear edge 124, which is designated as an end point 52 b. In other words, a position corresponding to the recessed portion 42 of the front edge 123 is used as the starting point 52 a, and a position on the rear edge 124 is used as the end point 52 b. In this case, as with the first ribs 51 described in the first embodiment, each of the second ribs 52 extends continuously from the starting point 52 a to the end point 52 b. The second ribs 52 are all identical in height h2, which is equal to the height h1 of the first rib 51 located in the outermost peripheral position.

In the case where the ribs 51 are provided on only the negative pressure surface 121 of the negative and positive pressure surfaces 121, 122 of each blade 12 as in the first embodiment, air flows from the rear edge 124 of each blade 12 are released along the ribs 51 on the side adjacent to the negative pressure surface 121, and are released following contracted flows on the side adjacent to the positive pressure surface 122. As a result, a direction of an air flow emitted from the rear edge 124 of the blade 12 and flowing on the side adjacent to the negative pressure surface 121 is different from a direction of an air flow emitted from the rear edge 124 of the blade 12 and flowing on the side adjacent to the positive pressure surface 122, and thereby a turbulence occurs in air flows emitted from the rear edge 124 of the blade 12.

In contrast, according to the present embodiment, the first ribs 51 are provided on each negative pressure surface 121, and, in addition, the second ribs 52 are provided on each positive pressure surface 122. The directions of air flows released from the rear edge 124 of the blade 12 thereby can be the same on the side adjacent to the negative pressure surface 121 and on the side adjacent to the positive pressure surface 122, and air flows released from the rear edge 124 of the blade 12 can be stable.

According to the present embodiment, a quantity of the recessed portions 42 of the serration 40, a quantity of the first ribs 51, and a quantity of the second ribs 52 coincide with each other, and the first ribs 51 and the second ribs 52 are provided to correspond to each other one on one. As a result, an effect of stabilizing air flows released from the rear edge 124 of each blade is maximally enhanced.

The second ribs 52 are preferably arranged to overlap with the first ribs 51 in the fan axial direction as in the present embodiment in terms of adjusting the directions of air flows, which are emitted from the rear edge 124 of the blade 12, to be the same on the side adjacent to the negative pressure surface 112 and on the side adjacent to the positive pressure surface 122.

Fifth Embodiment

A quantity of first ribs 51 and a quantity of the second ribs 52 are reduced as compared to the fourth embodiment according to the present embodiment. The other configurations of the present embodiment are in the same as those of the fourth embodiment.

As shown in FIG. 12, in the present embodiment, first ribs 51 are provided in only a part of the recessed portions 42 of the serration 40. Specifically, as with the second embodiment, the first ribs 51 are provided in every other recessed portion 42 of the recessed portions 42 arranged along a front edge 123. Therefore, the present embodiment yields the same advantageous effects as those in the second embodiment.

In addition, in the present embodiment, second ribs 52 are provided in only some of the recessed portions 42 of the serration 40. Specifically, the second ribs 52 are provided in the recessed portions 42 located in the first, second, and third positions from the outer peripheral side.

As described in the second embodiment, providing ribs on the surfaces of each blade 12 results in formation of additional fixed walls in air flows flowing on the surfaces. Consequently, additional vortexes are generated from the ribs. According to the present embodiment, the quantity of the second ribs 52 is made smaller than the quantity of recessed portions 42. Therefore, generation of additional vortexes from the second ribs 52 can be reduced, in comparison with the case where second ribs 52 are provided in all recessed portions 42.

In addition, in the present embodiment, the quantity of the second ribs 52 is smaller than the quantity of the first ribs 51. Furthermore, the quantity of the second ribs 52 in an outer peripheral portion of the serration 40 is larger than the quantity of the second ribs 52 in an inner peripheral portion of the serration 40. As described in the third embodiment, contracted flow is more likely to occur on the outer peripheral side of an axial fan 10 than on the inner peripheral side of the axial fan 10. Therefore, in a case where the quantity of the second ribs 52 is reduced, it is effective to provide more of the second ribs 52 in the outer peripheral portion of the serration 40 than in the inner peripheral portion of the serration 40.

Sixth Embodiment

A quantity of the first ribs 51 and a quantity of the second ribs 52 are reduced as compared to the fourth embodiment according to the present embodiment, similar to the fifth embodiment. However, the present embodiment differs from the fifth embodiment in that the quantity of the second ribs 52 is larger than the quantity of the first fibs 51.

As shown in FIG. 13, in the present embodiment, the first ribs 51 are not provided in recessed portions 42 located in the first, second, and third positions from the inner peripheral side but are provided in recessed portions 42 located in the first, second, third, and fourth positions from the outer peripheral side. In addition, the second ribs 52 are provided in recessed portions 42 located in the first, second, third, fourth, fifth, and sixth positions from the outer peripheral side, other than a recessed portion 42 located on the innermost peripheral side.

In this manner, in the present embodiment, the quantity of the first ribs 51 on the outer peripheral portion of the serration 40 is larger than the quantity of the first ribs 51 on the inner peripheral portion of the serration 40. Furthermore, the quantity of the second ribs 52 on the outer peripheral portion of the serration 40 is larger than the quantity of the second ribs 52 on the inner peripheral portion of the serration 40. Accordingly, the present embodiment provides the same effects as the third embodiment and the fifth embodiment.

Air flows that have passed on the negative pressure surface 121 of each blade 12 reach the positive pressure surface 122 of the next blade 12 in the rotating direction DR1 of the axial fan 10. As a result, the positive pressure surface 122 is more likely to be affected by contracted flow and turbulence than the negative pressure surface 121 when comparing between the negative pressure surface 121 and the positive pressure surface 122 of the blade 12.

Therefore, a quantity of the second ribs 52 is preferably larger than a quantity of the first ribs 51 as in the present embodiment in a case where the second ribs 52 are provided in a part of the recessed portions 42 of the serration 40. Accordingly, the directions of air flows flowing on the positive pressure surface 122 can be adjusted to be parallel to each other. As a result, the directions of air flows emitting from the rear edge 124 of the blade 12 can be the same on the side adjacent to the negative pressure surface 121 and on the side adjacent to the positive pressure surface 122, and thereby the air flows emitting from the rear edge 124 of the blade 12 can be stable.

FIG. 14 shows the measurement results of the noise levels of the axial blowers in the first embodiment, sixth embodiment, and comparative example. The axial blower J1 in the comparative example is obtained by eliminating the ribs 51 from the negative pressure surface 121 of the axial blower 1 according to the first embodiment. If the quantity of recessed portions 42 of the serration 40 is N, the quantity of the first ribs 51 of the axial blower 1 according to the first embodiment is N, which is equal to the quantity of recessed portions 42; the quantity of the first ribs 51 and the quantity of the second ribs 52 of the axial blower 1 according to the sixth embodiment are N-3 and N-1, respectively.

As shown in FIG. 14, it is found that the axial blower according to the first embodiment reduces noise more than the comparative example, and the axial blower according to the sixth embodiment reduces noise far more than the comparative example. As can be seen from the measurement results, the present embodiment is able to reduce noise most.

Seventh Embodiment

Next, a seventh embodiment will be described with reference to FIGS. 15, 16. FIG. 15 is a perspective view of each blade 12 according to the present embodiment. FIG. 16 is a cross-sectional view taken along a line XVI-XVI in FIG. 15. The line XVI-XVI in FIG. 15 is a curved line passing through the central part of a blade 12 in a circumferential direction (i.e., a chord direction). Therefore, FIG. 16 shows a cut section of the blade 12 when the blade 12 is cut in the central part in the circumferential direction (i.e., the chord direction).

The present embodiment differs from the first embodiment in that second recessed portions 53 are added to the positive pressure surface 122 of each blade 12. The present embodiment will be described while eliminating or simplifying portions identical or equivalent to portions in the first embodiment.

As shown in FIG. 15, in the present embodiment, as with the first embodiment, ribs 51 are provided on the side adjacent to the negative pressure surface 121 of each blade 12 so as to correspond to all the recessed portions 42 of the serration 40.

As described in the fourth embodiment, the side adjacent to the negative pressure surface 121 and the side adjacent to the positive pressure surface 122 of each blade 12 are likely to differ from each other in a direction of air flow. If the side adjacent to the negative pressure surface 121 and the side adjacent to the positive pressure surface 122 of each blade 12 differ in the direction of air flow, a three-dimensional vortex, which is a factor in noise generation, may occur when air flow on the side adjacent to the negative pressure surface 121 and air flow on the side adjacent to the positive pressure surface 122 cross at the rear edge 124 of the blade 12.

Therefore, as shown in FIG. 16, the second recessed portions 53, which recede toward the side adjacent to the negative pressure surface 121, are provided on the positive pressure surface 122 of each blade 12 so as to correspond to ribs 51 provided on the side adjacent to the negative pressure surface 121 of the blade 12. That is, in the present embodiment, the second recessed portions 53 are formed so as to correspond to all recessed portions (i.e., first recessed portions) 42 of the serration 40. Therefore, a quantity of the first recessed portions 42 and a quantity of the second recessed portions 53 in the serration 40 are equal to each other according to the present embodiment.

The function of each second recessed portion 53 is to rectify air flows on the side adjacent to the positive pressure surface 122 of each blade 12. In this case, each recessed portion 53 continuously extends from the first recessed portion 42 in the front edge 123 on the side adjacent to the positive pressure surface 122 of each blade 12, as a starting point 52 a, to the rear edge 124, as an end point 52 b. In other words, a position corresponding to the first recessed portion 42 in the front edge 123 on the side adjacent to the positive pressure surface 122 of each blade 12 is used as the starting point 52 a, and a position on the rear edge 124 is used as the end point 52 b. Each second recessed portion 53 in the present embodiment continuously extends from the starting point 52 a to the end point 52 b. Specifically, each second recessed portion 53 in the present embodiment extends in a circumferential direction around the fan axis CL1 of the axial fan 10.

In the present embodiment, each second recessed portion 53 is formed as a groove of V-shaped cross-section. In addition, in order to ensure the strength of each blade 12, it is preferable to set such that the width of each second recessed portion 53 is equal to or less than the width of a rib 51 and the depth of each second recessed portion 53 is equal to or less than half of the thickness of the blade 12.

Other configurations in the present embodiment are identical to those in the first embodiment. According to the configuration of the present embodiment, collisions of main flows including downward flows created by the serration 40 can be restricted by the ribs 51. Therefore, the effect of restricting separation of main flows in the serration 40 can be exhibited.

The present embodiment is configured such that the second recessed portions 53 are provided in the positive pressure surface 122 of each blade 12. Accordingly, air flows on the side adjacent to the positive pressure surface 122 of each blade 12 are fixed while flowing from the recessed portions 42 of the serration 40 toward the rear edge 124 of each blade 12 along the second recessed portions 53. As a result, a direction of air flow on the side adjacent to the negative pressure surface 121 of each blade 12 and a direction of air flow on the side adjacent to the positive pressure surface 122 of each blade 12 can be easily fixed to be parallel to each other. A three-dimensional vortex, which is caused when an air flow from the side adjacent to the negative pressure surface 121 intersects with an air flow from the side adjacent to the positive pressure surface 122 at the rear edge 124 of each blade 12, can be thereby prevented from occurring.

Consequently, generation of noise resulting from air flow turbulence on the surfaces of each blade 12 can sufficiently be restricted. Furthermore, since restriction of air flow turbulence on the surfaces of the blade 12 can contribute to restriction of drive torque of a motor 30, fan efficiency of the axial blower 1 can be improved.

Furthermore, in the present embodiment, the quantity of the ribs 51 and the quantity of the second recessed portions 53 are equal to the quantity of recessed portions 42 of the serration 40, and the ribs 51 and the second recessed portions 53 are provided so as to correspond to one another on a one-to-one basis. Accordingly, the effect of stabilizing air flows released from the rear edge 124 of each blade is maximally enhanced.

The second recessed portions 53 are preferably arranged to overlap with the ribs 51 in the fan axial direction as in the present embodiment in terms of adjusting the directions of air flows, which are emitted from the rear edge 124 of the blade 12, to be the same on the side adjacent to the negative pressure surface 112 and on the side adjacent to the positive pressure surface 122. This is effective in restricting decrease in the strength of each blade 12, resulting from formation of the second recessed portions 53.

(Other Modifications)

The present disclosure is not limited to the above-described embodiments and can be modified within the scope of the present disclosure.

(1) Both of the ribs (i.e., the first ribs) 51 and the second ribs 52 designate the recessed portions 42 as the starting point, designate and the rear edge 124 as the end point 51 b, 52 b, respectively, according to the above-described embodiments. However, as shown in FIG. 17, positions between the front edges 123 and the rear edges 124 of blades 12 may be used as end points 51 b, 52 b. That is, the first ribs 51 and the second ribs 52 have a shape extending in an entire length of the blade surface in the chord direction according to the above-described embodiments, however the first ribs 51 and the second ribs 52 may have a shape extending from the recessed portions 42 in a partial length of the blade surface in the chord direction.

Even in this case, the same effects as the above-described embodiments can be obtained since directions of air flows on the blade surfaces can be adjusted to be parallel to each other as compared to a case having no ribs 51, 52 in the blade surfaces 121, 122 of the blades 12. Both of the first rib 51 and the second rib 52 preferably have the end portions 51 b, 52 b respectively as an end portion of the rear edge 124 in terms of enhancing the effect adjusting the directions of the air flows on the blade surfaces to be parallel to each other.

In addition, in each of the foregoing embodiments, both the first rib 51 and the second rib 52 have the shape extending in the circular arc. However, other shapes extending toward the rear edge 124 also suffice. For example, the first rib 51 and the second rib 52 may a shape extending parallel to tangents passing through the starting points 51 a, 52 a of the ribs 51, 52 through which the respective circles pass having the fan axis CL1 as their centers. In this way, the first and second ribs 51, 52 may have a straight shape.

(2) In each of the foregoing embodiments, the starting point 51 a of the rib 51 (first rib 51) is located in the deepest portion of the recessed portion 42. However the starting point 51 a may be deviated from the deepest portion of the recessed portion 42 as long as the point 51 a is within a range in which the collision of the main flows F4 including the downward flows F5 created by the serration 40 can be prevented. This is the same for the starting points 52 a of the second ribs 52 in the fourth to sixth embodiments.

(3) A quantity of the ribs (i.e., the first ribs) 51 provided in a single blade 12 is more than one according to the above-described embodiments, however the quantity may be one. Similarly, a quantity of the second ribs 52 provided in a single blade 12 may be one. In this case, the first ribs 51 and the second ribs 52 are preferably arranged in a center portion of the serration 40 since directions of air flows flowing on the blade surface are different between the inner peripheral side and the outer peripheral side of the blade 12. The directions of air flows on the blade surface can be thereby adjusted to be parallel to each other as compared to a case having no rib 51, 52 on the blade surfaces 121, 122 of the blades 12, and the same effects as the above-described embodiments can be obtained.

(4) The ribs (i.e., the first ribs) 51 are provided in all blades 12 according to the above-described embodiments, however the first ribs 51 may be provided in only a part of the blades 12. Similarly, the second ribs 52 may be provided in only a part of the blades 12. Even in this case, the directions of air flows on the blade surface can be adjusted to be parallel to each other as compared to a case having no rib 51, 52 on the blade surfaces 121, 122 of the blades 12, and the same effects as the above-described embodiments can be obtained.

(5) In each of the foregoing embodiments, the serration 40 is provided in part of the front edge 123 of each blade 12. However, the serration 40 may be provided in the entire front edge 123. The tip portion 41 of each serration 40 has the shape of a triangle the apex of which is sharpened. However, the apex may have a round shape. Similarly, the recessed portion 42 of each serration 40 may have a shape the bottom of which is round.

(6) It does not matter whether the blades 12 in each of the foregoing embodiments are straight blades, forward blades, backward blades, or the like. In each type, the application of the present embodiment is effective in a case where the directions of air flows on the surfaces of the blades 12 are not uniform and the inner peripheral side and outer peripheral side of each blade 12 differ in the direction of air flow flowing on the blade 12.

(7) In each of the foregoing embodiments, the present disclosure is applied to the axial blower 1 that has the shroud 20 and the ring part 13. However, the present disclosure is also applicable to the axial blower 1 that has either the shroud 20 or the ring part 13 or that has neither the shroud 20 nor the ring part 13. That is, the present disclosure is applicable to any axial blower in which the directions of air flows on a blade surface of one blade differ according to positions on the blade surface in fan radial direction.

(8) In the seventh embodiment described above, each recessed portion 53 has the shape continuously extending from the front edge 123 of the side adjacent to the positive pressure surface 122 of each blade 12 to its rear edge 124. However, the recessed portion may have a shape part of which is discontinuous.

In addition, as described in the seventh embodiment, it is desirable to form the second recessed portions 53 in the positive pressure surface 122 of each blade 12 in correspondence with the ribs 51 provided on the side adjacent to the negative pressure surface 121 of the blade 12. However, at least one or more second recessed portions 53 suffice. For example, the quantity of the second recessed portions 53 may be smaller than the quantity of the ribs 51 by forming the second recessed portion 53 in correspondence with one of the adjacent ribs 51. The second recessed portion 53 is not limited to have an arc shape but may have a straight shape as long as directions of the air flows released from the rear edge 124 become the same on the side adjacent to the negative pressure surface 121 and on the side adjacent to the positive pressure surface 122 of each blade 12.

Furthermore, in the seventh embodiment, each second recessed portion 53 is formed as a groove having a V-shape in cross section. However, the second recessed portion 53 may be formed as a groove having a U-shape in cross section or as a groove having a tetragonal shape in cross section.

As with the second ribs 52 described in the fourth to sixth embodiments, the second recessed portions 53 described in the seventh embodiment are used to rectify air flows on the side adjacent to the positive pressure surface 122 of each blade 12. Accordingly, the second ribs 52 in the fourth to sixth embodiments may be replaced by the second recessed portions 53.

(9) In each of the foregoing embodiments, the blower according to the present disclosure is applied to an axial blower 1 that has an axial fan 10. However, the blower according to the present disclosure may be applied to a blower that has a fan such as a centrifugal fan or cross-flow fan.

(10) In each of the foregoing embodiments, the blower according to the present disclosure is applied to a cleaning module blower for cooling an engine. However, the blower according to the present disclosure may be applied to a blower used in an air-conditioner for a vehicle or may be applied to a blower for home use or industrial use other than vehicle use.

(11) The above-described embodiments are not unrelated to each other and can be combined with each other except for a case where the combination is clearly improper. In the above-described embodiments, it is to be understood that elements constituting the embodiments are not necessary except for a case of being explicitly specified to be necessary and a case of being considered to be absolutely necessary in principle. 

What is claimed is:
 1. A blower comprising a fan that has a plurality of blades and generates an air flow by rotating, wherein each of the plurality of blades has a front edge and a serration provided at least in a part of the front edge, the serration has tip portions and recessed portions, which are arranged alternately with each other, each of the plurality of blades has a negative pressure surface and one or more ribs protruding from the negative pressure surface, and each of the ribs extends from a corresponding one of the recessed portions, which is designated as a starting point, to a rear edge of a corresponding one of the plurality of blades.
 2. A blower comprising an axial fan that has a plurality of blades arranged around a fan axis and rotates around the fan axis, wherein each of the plurality of blades has: a negative pressure surface forming a blade surface on one side in a fan axial direction that is an upstream side in a flow direction of air; a positive pressure surface forming a blade surface on an opposite side of the negative pressure surface; a front edge located on a front side in a rotating direction; and a rear edge located on a rear side in the rotating direction, the front edge of each of the plurality of blades is provided with a serration that has tip portions and recessed portions, the tip portions and the recessed portions are arranged alternately with each other along the front edge, the negative pressure surface of each of the plurality of blades is provided with one or more ribs protruding from the negative pressure surface, and each of the ribs extends from a corresponding one of the recessed portions, which is designated as a starting point, to the rear edge.
 3. The blower according to claim 2, wherein the ribs are provided in the negative pressure surface, and the ribs are provided in only a part of the recessed portions.
 4. The blower according to claim 3, wherein in a serration forming area in which the serration is formed, a portion of the serration forming area located on an inner side of a center of the serration forming area in a radial direction of the axial fan is defined as an inner peripheral portion of the serration, and a portion of the serration forming area located on an outer side of the center of the serration forming area in the radial direction of the axial fan is defined as an outer peripheral portion of the serration, and a quantity of the ribs provided in the outer peripheral portion of the serration is larger than a quantity of the ribs provided in the inner peripheral portion of the serration.
 5. The blower according to claim 2, wherein the starting point is located in a deepest portion of the corresponding one of the recessed portions.
 6. The blower according to claim 2, wherein the ribs extend in a circumferential direction of a circle centering on the fan axis.
 7. The blower according to claim 2, wherein each of the ribs extends from the corresponding one of the recessed portions, which is designated as the starting point, to the rear edge, which is designated as an end point.
 8. The blower according to claim 2, wherein the ribs are provided in the negative pressure surface, and the ribs are designed to have a height that increases from an inner side toward an outer side in a radial direction of the axial fan.
 9. The blower according to claim 2, wherein the ribs provided in the negative pressure surface are first ribs, the positive pressure surface is provided with one or more second ribs protruding from the positive pressure surface, and each of the second ribs extends from a corresponding one of the recessed portions, which is designated as a starting point, to the rear edge.
 10. The blower according to claim 9, wherein a quantity of the second ribs provided in the positive pressure surface is more than one, and the second ribs are provided in only a part of the recessed portions.
 11. The blower according to claim 10, wherein in a serration forming area in which the serration is formed, a portion of the serration forming area located on an inner side of a center of the serration forming area in a radial direction of the axial fan is defined as an inner peripheral portion of the serration, and a portion of the serration forming area located on an outer side of the center of the serration forming area in the radial direction of the axial fan is defined as an outer peripheral portion of the serration, and a quantity of the second ribs provided in the outer peripheral portion of the serration is larger than a quantity of the second ribs provided in the inner peripheral portion of the serration.
 12. The blower according to claim 9, wherein a quantity of the second ribs is larger than a quantity of the first ribs.
 13. The blower according to claim 9, wherein the starting point of each of the second ribs are located in the deepest portions of the corresponding one of the recessed portions.
 14. The blower according to claim 9, wherein the second ribs extend in a circumferential direction of a circle centering on the fan axis.
 15. The blower according to claim 9, wherein each of the second ribs extends from the corresponding one of the recessed portions, which is designated as the starting point, to the rear edge, which is designated as an end point.
 16. A blower comprising an axial fan that has a plurality of blades arranged around a fan axis and rotates around the fan axis, wherein each of the plurality of blades has: a negative pressure surface forming a blade surface on one side in a fan axial direction that is an upstream side in a flow direction of air; a positive pressure surface forming a blade surface on an opposite side of the negative pressure surface; a front edge located on a front side in a rotating direction; and a rear edge located on a rear side in the rotating direction, the front edge of each of the plurality of blades is provided with a serration that has tip portions and recessed portions arranged alternately with each other, the tip portions and the recessed portions are arranged alternately with each other along the front edge, the negative pressure surface of each of the plurality of blades is provided with first ribs protruding from the negative pressure surface, the positive pressure surface of each of the plurality of blades is provided with second ribs protruding from the positive pressure surface, each of the first ribs and the second ribs extends in a circumferential direction of a circle centering on the fan axis, from a corresponding one of the recessed portions, which is designated as a starting point, to the rear edge, which is designated as an end point, in an area in which the serration is provided, a portion of the serration forming area located on an inner side of a center of the serration forming area in a radial direction of the axial fan is defined as an inner peripheral portion of the serration, and a portion of the serration forming area located on an outer side of the center of the serration forming area in the radial direction of the axial fan is defined as an outer peripheral portion of the serration, a total quantity of the first ribs and the second ribs provided in the outer peripheral portion of the serration is larger than a total quantity of the first ribs and the second ribs provided in the inner peripheral portion of the serration, and a quantity of the second ribs is larger than a quantity of the first ribs. 